Zodiac is the only free, open source MSX emulator for Mac OS X. It currently supports both disk images and MSX rom files. Zodiac uses the SDL library for cross platform compatibility and can be ported to almost any SDL supported platform in existence. It requires that you install the SDL libraries to work. MSX system ROMs also are available for download.

It is good to see another MSX emulator on the Mac, but Zodiac being only in the early development stage there are still a lot of functionalities to be improved. A few MSX1 and MSX2 titles did not start (e.g. F1 Spirit) and there seems to be serious problem with the arrow keys, not responding effectively. Sound support is average.
My recommendation would be to use fMSX 2.6 if you are running OS X or alternatively FreeM or fMSX 1.5 if you are on OS 9.
But, let's keep an eye open on Zodiac - which could soon become the reference MSX emulator on Mac.